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The Fya, Fy6 and Fy3 epitopes of the Duffy blood group system recognized by new monoclonal antibodies: identification of a linear Fy3 epitope.

Four new anti-Duffy murine monoclonal antibodies (MAbs): two anti-Fy6 (MIMA-107 and MIMA-108), one anti-Fya (MIMA-19) and one anti-Fy3 (MIMA-29) were characterized. Identification of epitopes by means of synthetic peptides (Pepscan) showed that the anti-Fy6 reacted most strongly with peptides containing the sequence 19QLDFEDV25 of the Duffy glycoprotein, and less strongly with peptides containing LDFEDV (MIMA-107) or LDF only (MIMA-108). The anti-Fya recognized epitope 38DGDYGA43 containing the Gly42 residue, which defines the Fya blood group antigen. MIMA-29 is the first anti-Fy3 reactive with a linear epitope 281ALDLL285 located in the fourth extracellular domain (ECD4, loop 3) of the Duffy glycoprotein. The four new antibodies extend the list of six anti-Fy MAbs formerly characterized by Pepscan analysis that allow some general conclusions. Fine specificities of various anti-Fya, or anti-Fy6 are not identical, but all of them recognize linear epitopes located around, respectively, Gly42 or between two potential N-glycosylation sites at Asn16 and Asn27. Anti-Fy3 recognize either a linear epitope located in ECD4, or a conformational epitope that includes amino acid residues of ECD4 and of other ECDs.

Animals↗

Long-term follow-up of indolent mastocytosis in adults.

OBJECTIVE: To evaluate the natural course of indolent mastocytosis in adults. DESIGN: A retrospective long-term follow-up study. SETTING: The Department of Endocrinology of a University Hospital. PATIENTS: Sixteen adult patients with a diagnosis of indolent mastocytosis and sufficient biochemical data for statistical analysis. One patient had paediatric-onset cutaneous mastocytosis, whilst the others had adult-onset systemic mastocytosis. Ages at the end of follow-up ranged from 23 to 79, median 50 years. Follow-up periods per patient lasted from 13 to 135 months, median 90 months. MEASUREMENTS: Urinary excretions of the histamine metabolites N tau-methylhistamine (MH) and N tau-methylimidazoleacetic acid (MIMA), and signs and symptoms of the disease. RESULTS: The excretion of MH but not MIMA increased in four patients (ages 37, 45, 61 and 65 years) and decreased in two patients (ages 26 and 48 years), including the only patient with paediatric-onset cutaneous mastocytosis. The excretion of MIMA but not MH increased in none and decreased in one patients (age 51 years). The excretions of both MH and MIMA increased in one patient (age 23 years) and decreased in two patients (ages 65 and 79 years). The excretion of MH and MIMA can be considered to have been stable in one patient (age 49 years). In the five remaining patients, observation periods were rather short. A definite judgement on the course of their disease could not be given. In the two patients in whom the excretion of both MH and MIMA decreased, the enlarged spleen decreased in size, whilst in the other patients, signs and symptoms did not change. There were no accompanying myeloproliferative disorders in any patient. No special treatment aiming at a reduction in mast cell load has been given. Rates of change over the whole follow-up period ranged from -8.4 to +25.1% per year. CONCLUSION: The natural course of indolent adult-onset mastocytosis is not always progressive. Our data show that the activity of adult-onset indolent mastocytosis, as measured by urinary excretion of MH and MIMA and clinical signs and symptoms, can substantially decline, especially in older patients.

Adult↗

A panel of monoclonal antibodies recognizing GPI-anchored ADP-ribosyltransferase ART4, the carrier of the Dombrock blood group antigens.

ART4 (CD297) is a member of the family of toxin-related ADP-ribosyltransferases (ARTs) and is the carrier of the Dombrock blood group alloantigens (Do). Two mouse monoclonal antibodies (MIMA-52 and MIMA-53), and two rat monoclonal antibodies (N0NI-B4 and NONI-B63) were obtained following immunization of mice with human Do/ART4-transfected cells and of rats with human Do/ART4 cDNA, respectively. All four mAbs recognize Do/ART4-transfected Jurkat cells but not untransfected cells by FACS analysis. Staining of Do/ART4-transfected cells by these mAbs was reduced following treatment of cells with PI-PLC, confirming that Do/ART4 is anchored in the cell membrane by linkage to glycosylphosphatidylinositol as predicted from its amino acid sequence. The four mAbs did not react with Gy(a-) (Dombrock null) erythrocytes but agglutinated other red blood cells. By flow cytometric analysis, all mAbs reacted prominently with erythrocytes, and weakly with peripheral blood monocytes and splenic macrophages, but not with B-lymphocytes or T-lymphocytes. The mAbs reacted weakly also with human umbilical vein endothelial cells and the basophilic leukemia KU-812. Immunohistology revealed staining of epithelia and endothelia on sections of tonsils. In FACS analyses NONI-B4 competed with MIMA-52 for binding to Do/ART4-transfected cells and erythrocytes, whereas NONI-B63 competed with MIMA-53. Neither of the mAbs reacted with mouse ART4-transfected cells, but NONI-B63 and MIMA-53 did react with a mouse/human ART4 chimera, indicating that the epitope recognized by these mAbs lies in the C-terminal half of the protein.

ADP Ribose Transferases↗

Production and characterization of anti-kell monoclonal antibodies using transfected cells as the immunogen.

Monoclonal antibodies (Mabs) to blood group antigens are valuable as diagnostic reagents for typing red blood cells (RBCs) in the clinical setting, and for structure-function studies of proteins. Here, we report a powerful system that enabled us to produce Mabs to blood group antigens. A murine erythroleukaemia (MEL) cell line expressing Kell protein, a transmembrane glycoprotein that carries a number of clinically relevant antigens, was used as a novel immunogen. Mabs with different specificities to the Kell protein were produced from a single mouse fusion: an anti-Jsb (MIMA-8), and two antibodies (MIMA-9 and MIMA-10) with novel specificities, that reacted with RBCs with the common Kell phenotype but not with RBCs with K+k- or Kp(a+b-) or K0 phenotypes. The non-reactivity with both K+k- or Kp(a+b-) RBCs implied that the epitope was influenced by the molecular changes associated with an absence of the k or Kpb antigens. MIMA-8 is the first example of a Mab anti-Jsb and was used in the clinical laboratory for screening donor RBCs for Js(b-) blood and for typing RBCs from patients even when the RBCs were coated with anti-IgG as is the case in autoimmune haemolytic anaemia. Heavy and light chain variable regions of MIMA-8 were cloned and the sequence is given. This study illustrates the potential of this novel immunization approach for making monoclonal antibodies to blood group antigens.

Animals↗